Shape memory alloys (SMA) have been applied to a wide variety of applications, in part, because of their ability to undergo a reversible phase transformation. It has been shown that the thermally induced martensite to austenite transformation of indented SMA allows for indent recovery on the microscale and nanoscale.
Many SMAs exhibit a one-way phenomenon, where, upon subsequent cooling (i.e. cooling after the initial shape memory effect is exhibited) from the austenite to the martensite phase, the SMA does not return to the previously deformed shape. As such, these materials may be limited in the applications in which they may be used.
Other SMAs exhibit a two-way phenomenon, where, upon subsequent cooling of the SMA from the austenite to the martensite phase, the SMA returns to the deformed or remembered shape. Two-way shape memory behavior may be realized in shape memory alloys via thermomechanical treatments, or training, which include thermomechanical cycling, aging under external stress, and plastic deformations. Despite the versatile available training methods, the basic mechanism of the two-way shape memory effects remains somewhat elusive. It is believed that residual martensite, dislocations resulting from training, or dislocations and their correspondent internal stress fields may cause the two-way effect. These methods are based on relatively simple loading conditions, such as uniaxial tensile, shearing, or bending, which may affect the stability and magnitude of the two-way shape memory behavior. While these methods allow two-way shape memory effects in the form of elongation, compression, torsion, and bending, these methods generally do not form shape memory surfaces with a variety of features.
As such, it would be desirable to provide other methods for forming a variety of two-way shape memory surfaces.